The operators of the ferris wheel would like to inject some more excitement into their rides and would like to increase the number of revolutions per minute . Their experience tells them that nausea can occur when riders are subjected to vertical speed in excess of 1m/s. Assist them by using mathematics to estimate the number of revolutions per minute the ferris wheel can go before running the risk of riders being sick all over the place ?

The wheels diameter is 20 metres and it takes 2 minutes to complete one counter-clockwise revolution. Rides last for three revolutions.

I found the h(t)= 10sin(pi/60 t -pi/2)+10

Apparently I can differentiate that to = 1/6 pi sin(pi/60 t)

then make the differentaited equation = 1

then i dont know the right answer for t because I keep getting different answers .

even so what does this t value mean in terms of the whole question ?

HELP PLEASE